Boats made as mentioned above do not have a central keel, and when they are propelled at high speed they plane, thereby causing them to be supported on the water solely via the rear portions of the two branches of the tube. Under such circumstances, they behave like catamarans.
A disadvantageous feature of such catamarans lies in the absence of guidance for liquid flow beneath the central portion of the boat, specifically where the arm of the outboard motor assembly plunges into the water. As a result the flow of water at this location is highly unstable and it is practically impossible to position appropriately the anticavitation plates that are fixed to the arm of the motor assembly above the thrust member(s).